Ceres: The Wet Look
The most recent insights come from a trio of astronomers led by Andrew S. Rivkin (Applied Physics Laboratory), who examined the big asteroid's near-infrared spectral signature last year. Previous work had already established the presence of clay-like minerals that include water as part of their molecular structure. Rivkin's team has used the body's infrared fingerprint to refine the kinds of materials that might lie on its surface. The best candidates, he reported at a recent meeting of planetary scientists, are iron-rich clays that contain roughly 5% carbonates just the kind of minerals that would form on what was once a wet surface.
Curiously, the surface exhibits no hint of water ice, which would be readily detected by infrared spectroscopy.
The new results follow on the heels of extensive observations with the Hubble Space Telescope, conducted last year, that imply Ceres is more than just a rocky jumble. Peter C. Thomas (Cornell University) and others determined that its slightly squashed shape and spin rate match what would be expected for a body that had differentiated (segregated) into a rocky core and a water-ice exterior. A thin rind of rock and dust may be all that's hiding an icy layer 60 to 120 kilometers (40 to 80 miles) thick.
According to Carry, the surface of Ceres displays a wealth of bright and dark markings, some of which might be due to regional differences in composition.
All of this is whetting the appetite of scientists involved in Dawn, a NASA spacecraft that narrowly avoided outright cancellation earlier this year. Now scheduled for launch next summer, Dawn will spend time orbiting both Ceres and Vesta, an equally intriguing asteroid.